amu has been replaced by u which is known as ….A here A refers to

Options

A. unified-mass
B. uni-mass
C. unitech-mass
D. unit-mass

Answer

To solve the question, we need to identify what "A" refers to in the context of the replacement of AMU by U.

### Step-by-Step Solution:

1. **Understanding AMU**:
- AMU stands for Atomic Mass Unit. It is a unit that was used to express atomic and molecular weights.

2. **Definition of AMU**:
- The definition of 1 AMU is based on the mass of carbon-12. Specifically, 1 AMU is defined as 1/12th of the mass of a carbon-12 atom.

3. **Replacement of AMU**:
- The term AMU has been replaced by the term "u", which stands for unified atomic mass unit.

4. **Meaning of "u"**:
- The unified atomic mass unit (u) is essentially the same as AMU but is more widely accepted in scientific literature.

5. **Identifying "A"**:
- In the question, "A" refers to the term that describes "u". Since "u" stands for unified atomic mass unit, "A" is also known as "unified mass".

6. **Conclusion**:
- Therefore, the answer to the question is that "A" refers to "unified mass".

### Final Answer:
A refers to "unified mass".